Electroplating



United States Patent G W ELECTROPLATING Donald Gardner Foulke, Watchung, and Otto Kardos,

Red Bank, N. J., assignors to Hanson-Van Winkle- Munning Company, a corporation or New .iersey No Drawing. Application November 16, 1956 Serial No. 622,531

4 Claims. (Cl. 204-49) This invention relates to electroplating and, more particularly, to electrodepositing nickel from an aqueous acidic nickel plating bath. The invention is based on our discovery that aromatic phosphinic acids, when incorporated in a nickel electroplating bath, particularly in conjunction with various sulfo-oxygen compounds, are capatale of promoting the formation of excellent bright and ductile electrodeposits of nickel over a wide current density range.

The electrodeposition of nickel from a plating bath containing a sulfo-oxygen carrier brightener additive yields deposits of limited intensity. Moreover, such brightness as is produced using such agents is obtained over only a limited current density range. When, however, a small quantity of an aromatic phosphinic acid is incorporated in the plating bath together with a sulfo-oxygen compound, the brightness capacity of the bath is extended and the electrodeposit is ductile and bright over a very wide current density range.

These aromatic phosphinic acids possess, as their common structural feature, the presence of a highly polar phosphinic acid group having the following structural formula:

Only relatively small quantities of the aromatic phosphinic acids are required in the plating bath, especially when used in conjunction with a sulfo-oxygen carrier brightener, for we have found that the highly polar phosphinic acid group appears to exert a pronounced synergistic effect on the brightening capacity of the sulfooxygen compound. In general, concentrations of the aromatic phosphinic acid as low as 0.05 gram per liter are effective. There appears to be no critical upper limit on the concentration of this phosphinic acid compound, but there is no advantage ordinarily in using more than 5 grams per liter, and in most plating baths substantially the full benefit of its presence is achieved with 3 grams per liter or less.

Any aromatic phosphinic acid, or alkali metal, magnesium, ammonium, and nickel salts of an aromatic phosphinic acid which is capable of being dissolved by acid and does not undergo decomposition upon protonation may be selected for inclusion in the plating solution. We have obtained particularly satisfactory results using a mononuclear or binuclear aromatic phosphinic acid, especially phenylphosphinic acid; but alkyl-substituted aromatic phosphinic acids may also be used with advantage in the plating bath.

A preferred process according to this invention for pro ducing bright nickel deposits comprises electrodepositing nickel from an aqueous acidic solution of at least one nickel salt, in which there is dissolved from about 0.05 to about 5 grams per liter of an organic phosphinic acid of the group consisting of mononuclear and; binuclear am- 2,839,453 Patented June 17, 1958 matic phosphinic acids, and from about Mr to about grams per liter of a water-soluble sulfo-oxygen compound of the group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononuclear aromatic sulfinic acids, the akali metal, magnesium, ammonium, and nickel salts of said acids, and mononuclear aromatic sulfonamides and sulfonimides.

Preparation of the aromatic phosphinicacids may be accomplished by initially reacting an aromatic hydrocan bon with phosphorus trichloride, in the presence of a Friedel-Crafts catalyst such as aluminum chloride, to form the aryldichlorophosphine. Hydrolysis of the aryldichlorophosphine results in the formation of the correspond ing aromatic phosphinic acid. Examples of the aromatic phosphinic acids which may be used successfully in embodiments of this invention are listed in Table I. Although these aromatic phosphinic acids may be used in concentrations as high as 5 grams per liter or even more, there is in most cases no particular advantage to be gained from concentrations in excess of 3 grams per liter, and they there fore are preferably used in the range of concentrations from about 0.1 to about 3 grams per liter.

TABLE I Organic phosphinic acids (1) Mononuclear aromatic phosphinic acids:

Phenylphosphinic acid, C H P(O) (OH)H o-, mor p-Tolylphosphinic acid, CH C H P(O) (OH)H 4-ethylphenylphosphinic acid, C H C H P0O) {0H)H 2,4-dimethylphenylphosphinic acid,

3)2 s 3 2,4,5- or 2,4,6-trimethylphenylphosphinic acid,

s)a e 2 2-methyl-5-isopropylphenylphosphinic acid,

3) a '1) s a -D Diphenylphosphinic acid, C H -C H P(O) (OH)H (2) Binuclear aromatic phosphinic acids:

Alpha-naphthylphosphinic acid, C I-I P(O) (OI-DH Beta-naphthylphosphinic acid, C H- P(O) (0H)H The compounds listed in Table II are examples of sul'fooxygen compounds which, when used in the plating bath in combination with the aromatic phosphinic acids, extend the current density range over which the formation of bright and ductile nickel deposits may be obtained. These sulfo-oxygen compounds may be used over a very wide range of concentrations (M1 to 80 grams per liter), but preferably are used in an amount in the range from about 1 to about 30 grams per liter.

TABLE II Organic sulfa-oxygen compounds (1) Unsaturated aliphatic sulfonic acids, and alkali metal, ammonium, magnesium, and nickel salts thereof:

Sodium vinyl sulfonate, H C=CHSO Na Sodium allyl sulfonate, H C=:CHCH SO Na (2) Mononuclear aromatic sulfonic acids, and alkali metal, ammonium, magnesium, and nickel salts thereof:

Benzene monesulfonic acid, C H SO H Sodium benzene monosulfonate, C H SO Na Nickel benzene monosulfonate, (C H5SO )gNl Sodium p-toluene monosulfonate, CH C H SO Na p-Chlcrobenzene sulfonic acid, CIC I-QSO H 3 Sodium p-chlorobenzene sulfonate, ClC H SO Na- Sodium p-bromobenzene sulfonate, BrC H SO Na 1,2-dichlorobenzene sulfonic acid, Cl C I-I SO I-I 1,2- or 2,5-dichlorobenzene sulfonates, sodium salt,

CI2CGH3SO3NZ1 m-Benzene disulfonic acid, C H (SO H) Sodium m-benzene disulfonate, C H (SO Na) Nickel m-benzene disulfonate, C H (SO );;Ni o-Sulfobenzoic acid monoammonium salt,

HOOC-C H SO NH 1-amino-2,5-benzene disulfonic acid, H NC H;(SO H) o-Aminobenzene sulfonic acid, H NC H SO H (3) Mononuclear aromatic sulfinic acids, and alkali metal, ammonium, magnesium, and nickel salts thereof:

Sodium benzene sulfinate, C H SO Na Sodium p-toluene sulfinate, CH C H SO Na (4) Mononuclear aromatic sulfonamides and sulfonimides: Benzene sulfonamide, C H SO NH p-Toluene sulfonamide, CH C H SO NH o-Sulfobenzoic imide Benzyl sulfonamide, CoHgCHgSOgNHQ Benzene sulfhydroxamic acid, C H SO NHOI-I N,N-dimethyl-p-toluene sulfonamide,

CH C l-I S N(CH N,N-dicarboxyethyl benzene sulfonamide,

C H SO N(C H COOH),

(5) Binuclear aromatic sulfonic acids, and alkali metal, ammonium, magnesium, and nickel salts thereof:

Z-naphthalene monosulfonic acid, C H SO H 1,5- or 2,7-naphthalene disulfonic acid, C H (SO H) Nickel 1,5- or 2,7-naphthalene disulfonate, C H (SO Ni Naphthalene trisulfonic acid, C H (SO H) Sodium naphthalene trisulfonate, C H (SO Na) 2-naphthol-3,6-disulfonic acid, HOC H (SO H) Sodium 2-naphthol-3,6-disulfonate, H0C H (SO Na);

1-naphthylamine-3,6,8-trisulfonic acid,

(6) Heterocyclic sulfonic acids, and alkali metal, ammonium, magnesium, and nickel salts thereof:

Thiophene sulfonic acid, C H S-SO I-I Sodium thiophene sulfonate, C H S-SO Na 2-(4-pyridyl)ethyl sulfonic acid, C H N.C H SO H For the most part, only free sulfonic acids are listed in Table II. However, the alkali metal, ammonium, magnesium, and nickel salts are in all cases the full equivalent of the acids, and may be used in their place in carrying out the process of this invention.

Table Ill summarizes the results of a series of tests which demonstrate the brightening effect on a Watts bath of various concentrations of representative sulfo-oxygen compounds, alone and in combination with phenylphosphinic acid. In each of these examples, a typical Watts plating bath having the following basic composition was used:

Grams per liter Nickel sulfate, NiSO -7H O 300 Nickel chloride, NiCl -6H O 45 Boric acid, HaBo 40 Plating operations in each example were carried out in a Hull test cell on brass cathodes so that the effect of a wide range of current densities could be observed. The pH of 4 the bath was adjusted to 3.5, and the electrodeposits were formed at a temperature of 50 C.

As a general rule, the use of an aromatic phosphinic acid in the plating bath, especially in combination with a sulfooxygen compound of the character described, has a leveling efiect, i. e. it results in nickel electro-deposits which are smoother than the underlying metal surface. By way of illustration, a nickel electrodeposit of 0.001 inch was formed on a roughened steel panel using a standard sulfate-chloride-boric acid bath containing 15 grams per liter of sodium naphthalene-1,3,6-trisulfonate, 0.24 gram per liter of phenylphosphinic acid and 0.02 gram per liter of a low-foaming wetting agent. The plating operation was conducted at a temperature of 50 C. and at a current density of 40 amperes per square foot. Mild air agitation of the bath was provided. Prior to plating, the roughness value (root mean square value in microinches) of the steel panel, obtained with a Brush Surface Analyzer, was 17 to 18 microinches. Following the plating operation, however, the surface roughness of the panel had been reduced to 7 to 8 microinches.

In the aforementioned examples of the invention, the brightener additions were used successfully on the stand ard Watts nickel electroplating bath. However, these brightener additions are also eifective in other acid nickel electroplating baths.

We claim:

1. The process for producing bright nickel deposits which comprises electrodepositing nickel from an aqueous acidic solution of at least one nickel salt in which there is dissolved from about 0.05 to about 5 grams per liter of an organic phosphinic acid of the group consisting of mononuclear and binuclear aromatic phosphinic acids, and from about /1, to about grams per liter of a water-soluble sulfo-oxygen compound of the group con sisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononuclear aromatic sulfinic acids, the alkali metal, magnesium, ammonium, and nickel salts of said acids, and mononuclear aromatic sulfonamides and sulfonimides.

2. The process for producing bright nickel deposits which comprises electrodepositing nickel from an aqueous acidic solution of at least one nickel salt in which there is dissolved from about 0.1 to about 3 grams per liter of phenylphosphinic acid, and from about 1 to about 30 grams per liter of a water-soluble sulfo-oxygen compound of the. group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononuclear aromatic sulfinic acids, the alkali metal, magnesium, ammonium, and nickel salts of said acids, and mononuclear aromatic sulfonamides and sulfonimides.

3. An aqueous acidic nickel electroplating bath in which there is dissolved from about 0.05 to about 5 grams per liter of an organic phosphinic acid of the group consisting of mononuclear and binuclear aromatic phosphinic acids, and from about A to about 80 grams per liter of a water-soluble sulfo-oxygen compound of the group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, heterocyclic sulfonic acids, mononu-clcar aromatic sulfinic acids, the alkali metal, magnesium, ammonium, and nickel salts of said acids, and mononuclear aromatic sulfonamides and sulfonimides.

4. An aqueous acidic nickel electroplating bath in which there is dissolved from about 0.1 to about 3 grams per liter of phenylphosphinic acid, and from about 1 to about 30 grams per liter of a water-soluble sulfo-oxy-gen com- 6 pound of the group consisting of unsaturated aliphatic sulfonic acids, mononuclear and binuclear aromatic sulfonic acids, hetcrocyclic sulfonic acids, mononuclear aromatic sulfinic acids, the alkali metal, magnesium, ammonium, and nickel salts of said acids, and mononuclear aromatic sulfonamides and sulfonimides.

Knapp ct al Apr. 29, 1952 Brown Oct. 6, 1953 

1. THE PROCESS FOR PRODUCING BRIGHT NICKEL DEPOSITS WHICH COMPRISES ELECTRODEPOSITING NICKEL FROM AN AQUEOUS ACIDIC SOLUTION OF AT LEAST ONE NICKEL SALT IN WHICH THERE IS DISSOLVED FROM ABOUT 0.05 TO ABOUT 5 GRAM PER LITER OF AN ORGANIC PHOSPHINIC ACID OF THE GROUP CONSISTING OF MONONUCLEAR AND BINUCLEAR AROMATIC PHOSPHINIC ACIDS, AND FROM ABOUT 1/4 TO ABOUT 80 GRAMS PER LITER OF A WATER-SOLUBLE SULFO-OXYGEN COMPOUND OF THE GROUP CONSISTING OF UNSATURATED ALIPHATIC SULFONIC ACIDS, MONONUCLEAR AND BINUCLEAR AROMATIC SULFONIC ACIDS, HETEROCYCLIC SULFONIC ACIDS, MONONUCLEAR AROMATIC SULFINIC ACIDS, THE ALKALI METAL, MAGNESIUM, AMMONIUM, AND NICKEL SALTS OF SAID ACIDS, AND MONONUCLEAR AROMATIC SULFONAMIDES AND SULFONIMIDES. 